Abstract
Protocols for the synthesis of C7 -nitropurine nucleosides and nucleotides are described. Each of these nucleotides
can completely replace its naturally occurring counterpart in polymerase chain reaction
(PCR), generating amplified duplex DNA containing nitropurines. As predicted, the
electron-withdrawing power of the nitro group rendered these modified oligonucleotides
susceptible to chemoselective cleavage at the modified bases. Treatment with secondary
amines at elevated temperatures produced selective DNA scission at nitropurine sites.
Interestingly, this Maxam-Gilbert type of DNA cleavage reaction was facilitated by
the addition of tris(2-carboxyethyl)phosphine (TCEP), a strong reducing agent and
nucleophile. Mass spectrometry analysis not only confirmed that DNA cleavage occurred
at the nitropurines, but also revealed that the fragmented DNA products are appended
by a TCEP moiety at its 3′-end. This surprising result provided new insights into
the mechanisms of such DNA cleavage reactions.
Key words
cleavage - nucleotides - oligonucleotides - nucleophilic additions - regioselectivity
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